During digital real-time signal analysis in the time domain it is important to know the phase shift of the signal to be tested with respect to the reference signal. Deviations in the phase shift between these two signals lead to reduced accuracy in the determination of the signal parameters.
The relative phase shift of signals is the phase difference, that is to say the time displacement, of the signals in relation to one another. From Tietze U., Schenk Ch. “Halbleiter-Schaltungstechnik” [Semiconductor Circuit Engineering], 10th edition, p. 956, it is known to detect the phase by means of a sample and hold element, by the voltage of a signal at the time of the zero crossing of a reference signal being switched to a capacitor and the voltage on the capacitor indicating a measure of the phase.
A measurement of the relative phase shift of digital signals by using a capacitor, which represents a delay element, would slow the measurement at high frequencies, for example in the range from 1 MHz to 10 MHz, and the measurement would not be able to be performed in real time. In addition, during the measurement of relative phase shifts of digital signals with such high frequencies, a high sampling rate and, at the same time, a good resolution are required. At a signal frequency of 10 MHz and a required 1000 sampled values per period, the sampling frequency would have to be 1000*10 MHz=10 GHz. Such a high sampling frequency cannot be implemented in many applications.